Cleaning method and apparatus with dense phase fluid

ABSTRACT

The invention relates to a cleaning apparatus which uses as operative fluid liquid and/or supercritical carbon dioxide (CO 2 ) or other dense-phase fluids such as ammonia or hydrocarbons. The apparatus may have various applications including the cleaning of garments and the degreasing of electronic or mechanical components; the apparatus comprises a cleaning chamber ( 1 ), basically formed by a pressurised container, and an installation for supplying the CO 2  which includes a storage tank ( 30 ) and a distiller ( 31 ). Advantageously, in order to start a cleaning cycle, the chamber ( 1 ) is pressurised with gaseous CO 2  taken from the tank and/or from the distiller which are then excluded from the path of the liquid CO 2  used for the actual cleaning. The invention also comprises a special cleaning chamber ( 1 ) having a lid and a cylindrical jacket, that are provided with respective mating edges between which operates an improved seal suitable for preventing leakage of supercritical fluids.

The present invention relates to cleaning apparatuses in which a densephase fluid, such as, for example, liquid and/or supercritical carbondioxide (CO₂), is used as operative fluid.

Before proceeding further, it should be pointed out that in the text ofthis description and in the following claims, the generic expression“dense phase” is intended to define the various phases in which a highpressure fluid may be and which include the liquid phase as well as thesubcritical and supercritical phases.

It is also important to state beforehand that, although reference willbe made in this description mainly to carbon dioxide as the operativecleaning fluid, the matters that will be set forth are to be understoodas being valid also for other fluids, such as, for example, ammonia andsome hydrocarbons which may be used in cleaning apparatuses manufacturedin accordance with the principles that will become clear hereinafter.

The mentioned apparatuses were developed fairly recently within theframework of special aims, such as the dry-cleaning of garments andtextile fibres in general, and the degreasing and cleaning of electroniccomponents or mechanical parts in general. There is already a largenumber of scientific publications and patents dealing with this subjectand, for all of them, reference will be made here only to U.S. Pat. No.5,467,492, whose proprietor is Hughes Aircraft Company.

More generally, it may be stated that nowadays the use of dense-phasecleaning fluids and in particular carbon dioxide, is gaining increasingimportance for various reasons which include among others theconsiderable qualities of this gas as a solvent when it is in the liquidor supercritical state, its non-toxicity and the absence of effects onthe environment when it has to be disposed of, since it is possible toexpel it freely into the atmosphere without causing pollution.

Mention should also be made of the fact that CO₂ is available naturallyat no cost and that, owing to its physical properties, it can be used incleaning cycles at ambient temperature (typically from 0 to 40° C.).

Owing to these characteristics, carbon dioxide is able to replace allthose solvents currently used in the dry-cleaning of clothing or in theother applications mentioned above that are based on perchloroethylene(PCE), derivatives of petroleum or chlorofluorocarbons (CFCs).

The apparatuses mentioned above, although intended for a variety ofpurposes, comprise a cleaning chamber which accommodates the objects tobe cleaned, irrespective of whether these are items of clothing,electronic components, mechanical parts or other.

These chambers are connected to an installation which supplies liquid orsupercritical CO₂ and which contains the means necessary for theproduction and circulation thereof, together with various filters forseparating it from the (solid, liquid or gaseous) substances which itremoves from the objects to be cleaned; the chambers in question maycontain drums or baskets, especially in the case of washing machines forgarments, or supports of various types on which the objects are placed.

In order to obtain apparatuses wherein carbon dioxide in the liquid orsupercritical state can circulate with the temperatures mentioned above,it is necessary to have operating pressures of the order of tens of bars(usually from 30 to 80 bar).

It will be appreciated that this requires accurate design andmanufacture of the apparatuses, and all the more so if it is borne inmind that they may be used under safety conditions that are notparticularly accurate or by persons without special training, such as,for example, in the case of clothes washing machines advantageouslyapplied in ordinary commercial laundries.

Since the specific interest in carbon dioxide cleaning apparatuses hasdeveloped only recently, they have not yet been manufactured on anindustrial scale; in other words, the cleaning apparatuses currentlyknown are basically prototypes and are therefore not specifically suitedto a practical use such as these put forward above.

Moreover, these prototypes do not generally have large dimensions and,in addition, even the patents mentioned in the introduction provide onlygeneral information on process aspects and do not go into any greaterdetail about the structure of the apparatuses.

Considering now U.S. Pat. No. 5,467,492, which has already been referredto, this patent provides only a schematic illustration of an apparatuswhere a cleaning chamber is connected to an installation which comprisesa CO₂ tank, a separator (or distiller), a condenser and a circulationpump.

The patent concentrates principally on aspects relating to the agitationof the items of clothing present in the cleaning chamber in order toobtain better cleaning thereof, but does not provide useful informationon how the apparatus actually functions.

This is not of secondary importance because, as it has already beenstated, it is necessary to operate with a high pressure fluid and thisfact therefore involves substantial difficulties.

For example, it is not clear from that document how the initialtransitory start-up state of the apparatus occurs, after the garments tobe cleaned have been loaded into its cleaning chamber; in thatsituation, the chamber is at atmospheric pressure and if liquid CO₂coming from the associated tank is introduced thereinto it as shown bythe diagram referred to, i.e. with a pressure from 35 to 70 baraccording to the information given in the patent, then the resultingexpansion causes sudden cooling of the chamber and the clothes presenttherein, with the risk that they will be damaged. The preheater providedin the apparatus could perhaps be used to avoid that risk, but thedescription does not explain how the preheater is to operate and in factit gives rise to several uncertainties regarding its actualeffectiveness in preventing the above-mentioned risk. EP-A-0,828,020discloses a washing method and a related apparatus, based on pressureswing absorption with a supercritical fluid; in this prior documentthere are general features of a washing apparatus working with liquidCO₂ but not the draining thereof.

Moreover, in this document the cleaning chamber is shown purelyschematically; it must not be forgotten that the chamber represents avery important part of these apparatuses.

Indeed, it has to provide for the necessary sealing at the highoperating pressures and must at the same time be easy to open and closewith a high degree of operator safety; this concerns the commerciallaundries already mentioned where there are a large number of successiveoperating cycles of the apparatus with the opening and closing of thechamber. Each time, an operator has to check that the chamber is closedcorrectly or that the pressure has fallen to a suitable level beforebeing able to open it.

Although it is clear that the apparatuses are provided with a suitablemonitoring system, the possibility of breakdowns or malfunctions shouldnot be overlooked and therefore it may be said that arrangements forgreater security can never be enough.

The object of the present invention is therefore to provide a cleaningmethod carried out with a carbon dioxide apparatus of the typeconsidered above, whose features satisfy the requirements of thepractical applications for which such cleaning is intended.

The object is achieved by a method whose technical features are set outin the claims appended to this description; the invention also includesan apparatus for carrying out the method, the features thereof are alsocontained in the above-mentioned claims.

The invention will be better understood in the light of the descriptiongiven hereinafter which relates to a preferred, non-limiting embodimentthereof, illustrated in the appended drawings wherein:

FIG. 1 is a diagram of an apparatus according to the invention;

FIG. 2 is an axonometric view of a cleaning chamber incorporated in theapparatus of FIG. 1, in the open state;

FIG. 3 is a longitudinal sectional view of the cleaning chamber of FIG.9;

FIG. 4 is a sectional view of a detail of the cleaning chamber mentionedabove, taken along a plane passing through the longitudinal axis “L” ofthe chamber and perpendicular to the plane of FIG. 3;

FIG. 5 shows in detail a seal of the previous cleaning chamber, in thenon-operative state;

FIG. 6 is an axonometric view of a variant of the cleaning chamber shownin the previous Figures;

FIG. 7 is a top view of the cleaning chamber of FIG. 6;

FIG. 8 is a longitudinal sectional view of a compressor present in thecleaning apparatus according to the invention;

FIG. 9 is a longitudinal sectional view of a distributor of liquid CO₂associated with the compressor of FIG. 8;

FIG. 10 is a sectional view taken along line X—X of FIG. 9.

Likewise it is commonly known, the apparatus of FIG. 1 comprises acleaning chamber 1, which will be discussed more comprehensivelyhereinafter, a tank 30 for liquid CO₂, a distiller 31 for separating thesubstances dissolved in the CO₂, a refrigerating unit 32 for keeping thecirculating fluid in the required conditions, and a main pump 33.

In addition, the apparatus of FIG. 1 contains a primary 34 and asecondary 35 filter, a compressor 36, a vacuum pump 37 and two heaters38, 39.

All these components are also connected by a hydraulic circuit whichcomprises numerous valves indicated in the diagram of FIG. 1 (althoughnot numbered) for the circulation of the liquid carbon dioxide in thecleaning apparatus; the circulation will be explained hereinafter inconnection with the carrying out of a cycle for cleaning garments. Itwill be appreciated, however, that the same points will apply also tothe cleaning of mechanical or electronic components and the like.

When the load to be cleaned is introduced into the chamber 1, the latteris isolated, for obvious reasons, from the portions of the circuit wherepressurised CO₂ is present by closing the necessary valves.

Once filled, the cleaning chamber 1 is closed and the pump 37 creates avacuum inside it; preferably, the level of vacuum reached should be atleast approximately 80 mbar in order to be able to remove the airpresent in the chamber and in the fibres of the clothing thusfacilitating the penetration of the CO₂ into the clothing and minimising(practically eliminating) the presence of incondensables in the cleaningfluid.

Thereafter the chamber 1, which has in the meantime been brought intocommunication with the remainder of the circuit from which it hadpreviously been isolated, is pressurised.

In order to cause the pressure level to rise without the disadvantagesmentioned above (sudden evaporation of the CO₂ and cooling of the load),CO₂ is initially introduced in the chamber in gaseous phase (instead ofin liquid phase); advantageously, the CO₂ is first taken from thedistiller 31 where it is available at a pressure lower than that in thetank 30.

This takes place as long as the difference in pressure P between thechamber 1 and the distiller 31 does not decrease in such a manner as tomake the flow of carbon dioxide too slow, thereby prolonging theoperation excessively; for example, a minimum value used in practice forP is approximately 3 bar.

After this first pressurisation step, further gaseous CO₂ coming fromthe upper portion of the tank 30 where it is in equilibrium with itsliquid phase, is introduced into the chamber 1 since, in the cleaningapparatus of this example, the tank 30 is under a pressure greater thanthat the distiller 31, especially when CO₂ has already been taken fromthe latter in order to pressurise the chamber.

In this connection, it should also be pointed out that according to apreferred embodiment of the invention, the tank 30 is connected to thedistiller 31 so that the liquid CO₂ present at the bottom of the formercan flow into the latter, taking advantage of the difference in pressureexisting between them; by doing that, it is possible in the distiller toseparate the CO₂ from the heavier oils present at the bottom of the tankor from any particles deposited there.

In order to promote separation, it is advantageous to heat the CO₂ whichgoes out of the tank 30 by means of the heater 38, because it is thuspossible to minimise the energy absorption peaks which would occur ifthe CO₂ were heated directly in the distiller 31.

When the pressurisation of the cleaning chamber 1 has been completed,preferably when the value of the pressure inside it is stillsufficiently lower than that in the tank 30, the cleaning chamber 1 isfilled with liquid CO₂ coming from said tank.

In this stage, the main pump 33 is active and, in accordance with apreferred embodiment of the invention, the filling of the chamber takesplace in two stages; during the first one, the chamber 1 does notevacuate and the CO₂ does not flow downstream thereof; that is to say,circulation takes place from the tank 30 to the chamber 1 by means ofthe pump 33: in this manner the risk of applying an excessive pressureto the primary filter 34 is avoided.

In a second stage, the chamber 1 is brought into communication with theprimary filter 34 and CO₂ circulation is established in the apparatusthrough, in succession, the pump 33, the chamber 1, the secondary filter35 and the main filter 34, the refrigerating unit 32, the tank 30 andthen, again, the pump 33.

When the liquid CO₂ has reached the predetermined level for starting theactual cleaning operation, the tank 30 is excluded from the path of thefluid which passes through the chamber 1, as was previously thedistiller 31; this takes place for a predetermined lapse of time (timingmeans not indicated in the diagram of FIG. 1 are indeed present in theapparatus) during which the circulation of CO₂ occurs only along thering formed by the pump 33, the chamber 1, the filters 35 and 34, therefrigerating unit 32 and, again, the pump 33.

This ensures regular CO₂ circulation which can best be controlled byadjusting the pump in such a manner as to improve the efficiency of theinflow of cleaning fluid into the chamber 1 and therefore of the actionproduced thereby on the garments to be cleaned.

Under these circumstances, it just has to be pointed out that thechamber 1 is provided with nozzles for supplying liquid CO₂, whichnozzles may be of various types depending on the methods by whichcleaning is carried out; in this connection, reference should be made tothe above-mentioned US patent purely for an indication of some of thepossible technical solutions available.

It is also evident that these solutions can vary depending on the typeof use intended for the apparatus; thus, for example, it will beappreciated that if garments are being cleaned, the nozzles will differfrom those used for degreasing mechanical parts or for treatingelectronic components.

Once the cleaning cycle just described has been completed, thecirculation of liquid CO₂ referred to above is interrupted; the chamber1 is then emptied, leaving the pump 33 in operation so that it returnsthe liquid CO₂ to the tank 30 which in the meantime has been inserted inthe path of the fluid again.

Advantageously, in order to compensate for the reduction in pressureinside the chamber 1, gaseous CO₂ coming from the upper portion of thetank 30 is caused to flow into the chamber 1; such compensation couldalternatively be provided for by using the gaseous phase present in thedistiller 31.

Finally, in accordance with a preferred embodiment of the invention, theload present in the cleaning chamber 1 is dried before the chamber isopened because, when the garments have been cleaned, they remainimpregnated with liquid CO₂ which, if there were a sudden reduction inthe pressure inside the chamber, could evaporate, thus bringing aboutsudden cooling of the load with freezing and weakening thereof and thusthe risk of damage by breaking.

The drying operation is carried out by circulating gaseous CO₂ takenfrom the top of the cleaning chamber 1 by means of the compressor 36 andheated in the heater 39; the heated CO₂ is then reintroduced into thechamber 1 through nozzles arranged on the base thereof.

When the temperature in the chamber 1 ensures that there is no moreliquid-phase CO₂ there, and this occurs when the temperature starts toincrease because it can be inferred therefrom that the change of phaseof all the liquid CO₂ is completed, it is possible to recover thegaseous CO₂.

In the apparatus according to the invention, this operation is carriedout by the compressor 36 which, in a preferred embodiment, is operatedwith liquid CO₂ coming from the tank 30; the compressor will bedescribed in more detail later on.

The compressor 36 sends the gaseous CO₂ to the tank 30 until asufficiently low pressure is reached in the chamber 1 which will bedetermined in accordance with the best method of carrying out theoperating cycle, that is to say, on the basis of a comparison betweenthe economic advantage of recovering the CO₂, on the one hand, and theduration, as well as the cost, of the cleaning cycle, on the other.

The residual CO₂ present in the chamber is then evacuated through anormal outlet valve connected to the chamber, after which it is possibleto open the chamber.

It will be appreciated from the above description that the cleaningapparatus according to the invention fully achieves the initiallydetermined object.

The stages making up the cleaning process ensure correct operation ofthe apparatus by means of which the process is carried out and take intoaccount the actual problems encountered in the handling of liquid orsupercritical CO₂.

For example, the application of the initial vacuum in the cleaningchamber 1 prevents the ambient air present inside it from circulating inthe installation for the CO₂: if it is borne in mind that these chambersmay have capacities of some hundreds of litres, it will be appreciatedthat the presence of such a volume of air could be disadvantageous.

Naturally, a small amount of air will nevertheless be present at thestart of each cycle in the CO₂ circuit but, because it is in a limitedamount owing to the initial vacuum, it can be easily disposed by usingsimple discharge valves suitably arranged in the apparatus.

As regards the pressurisation of the cleaning chamber, its operationwith gaseous CO₂ available in the distiller 31 and/or in the tank 30constitutes an entirely advantageous solution both from the design pointof view and from the economic point of view.

It will be first appreciated that best use is thereby made of twocomponents of the apparatus, that have to be used for its operationanyway: consequently, it is not necessary to have special means forcarrying out the pressurisation of the chamber or other systems forpreventing the risks associated with the sudden inlet of liquid-stateCO₂ into the cleaning chamber when it is under low pressure. Further tosimplifying the apparatus, all the above also contributes to a reductionin costs.

Finally, it should be mentioned that the recovery of gaseous CO₂ bymeans of the compressor operated with liquid CO₂ is also a substantialinnovation which makes this operation advantageous and efficient; therecovery of gaseous CO₂ is an operation which would not make sense interms of economy of the cleaning cycle if carried out with extensive useof equipment and energy because CO₂ gas is readily available naturallyand can also be discharged freely into the atmosphere.

By using the liquid CO₂ from the tank to operate the compressor, notonly there is a reduction in energy consumption but also the CO₂recovered is prevented from being contaminated with the lubricant whichis normally used in traditional compressors.

There are of course variants of the apparatus according to the inventionwith respect to the example which has been provided above.

Indeed, it will be appreciated that the diagram of FIG. 1 representsonly a simplified version of the apparatus in order to facilitateunderstanding thereof; actually, however, a large number of othercomponents will be provided also in accordance with the various possibleuses of the apparatuses.

In this connection, it should be pointed that the cleaning cycleaccording to the invention can also take place with the addition ofadditives to the dense-phase fluid; the additives may be of varioustypes depending on the several applications of the invention andtherefore the methods or the times by/at which they are introduced intothe cleaning cycle, will vary from case to case.

For example, in order to solubilise contaminants present in the load tobe cleaned (regardless of whether the load is composed of garments,parts to be degreased or other items) water or ethanol may be added tothe CO₂, while, in order to cause physical or microbiological particlesto be detached from the load, surfactants may be used; in the same way,in order to eliminate germs by chemical inactivation of themicro-organisms concerned, additives such as glutaraldehyde orquaternary ammonium salts may be used.

Finally, in order to increase the efficiency of the additives justdescribed or also as an alternative thereto, the cleaning cycledescribed above could also be integrated with operations forinactivating undesired micro-organisms by a physico-chemical method.using plasma or radicals of sterilising agents such as hydrogen peroxide(H₂O₂), ultraviolet rays, or the like.

Therefore, in such circumstances, the cleaning cycle using CO₂ could befollowed by a sterilising treatment carried out in the same apparatus:it will be appreciated that it would then be necessary to provide thenecessary means (H₂O₂ supply, radiant lamps, etc.) in order to carry outthe operations of normal cleaning with liquid CO₂ and sterilisingtreatment, which means are not present in the simplified version of theapparatus described above.

It should not be forgotten that the apparatus according to the inventionmay also comprise systems for detaching particles from the load to becleaned, such as, for example, emitters of ultrasound or other types ofvibration and pulsation in general.

Referring now to what has been initially stated, a description will nowbe given, with reference to FIGS. 2 to 7, of a specific cleaning chamberaccording to this invention which can be used preferably, but notexclusively, with the apparatus already considered.

This chamber 1 comprises a cylindrical jacket 2 with a longitudinal axisL arranged horizontally, which is provided at the rear with a convexbottom 3 and at the front with a lid 4 also convex.

In order to close the chamber 1, the cylindrical jacket 2 is providedalong half of its circular mouth with an edge 5 having a substantiallyC-shaped cross-section (see FIG. 4); inside the edge there is a step 6engaged by a rib 7 a, which extends circumferentially along the outeredge of the half of the lid 4 to be coupled with the above-mentionededge 5. As will be seen more clearly hereinafter, the coupling betweenthe step 6 and the rib 7 a constitutes an important safety element forthe operation of the chamber 1.

The edges 8 and 9 of the remaining halves of the mouth of thecylindrical jacket 2 and of the lid 4, have respective cross-sections ofa shape substantially reversed relative to that of the other halves.

Consequently, the lid 4 has a C-shaped edge 9 similar to that alreadyseen above, into which the edge 8 of the mouth of the jacket 2 extendsby projecting radially towards the outside. It should be pointed outthat, for the sake of simplicity in the Example illustrated here, theedges 8 and 9 have no steps and ribs of the type referred to above:however, steps and ribs could be provided by forming them in a positioninverted relative to the others, that is to say, on the lower face ofthe edge 8 and on the face, juxtaposed therewith, of the edge 9.

Sealing between the cylindrical jacket 2 and the lid 4 is ensured in thechamber 1 by a seal 10 arranged along the mouth of the cylindricaljacket in a suitable recess 11 extending circumferentially along theedge of the cylindrical jacket, and is activated by a fluid fed throughducts 12 shown with a broken line in FIG. 3 only. The fluid may beindependent and may therefore be fed through its own, separate, circuitor may be a fraction of the cleaning CO₂, which is caused to circulatein the recess 11 in order to activate the seal 10.

More specifically, the seal and the recess are of the type having across-section tapering towards the lid, which is already known and usedfor sterilisation autoclaves; however, unlike known seals, the seal 10is made from a suitable material that is resistant to carbon dioxide inthe liquid state and, above all, in the supercritical state.

Surprisingly positive results as regards sealing have been obtainedusing seals based on epichlorohydrin rubbers; these rubbers consist ofsaturated aliphatic polyether and chloromethyl side groups.

Homopolymeric rubbers have the following structural formula:

while copolymeric rubbers (a copolymer of epinchlorohydrin and ehtyleneoxide) have the structural formulae:

The seals produced using such materials have demonstrated the requiredcompatibility with CO₂ and have above all exhibited a high degree ofimpermeability to supercritical carbon dioxide.

Supercritical carbon dioxide is a very special fluid having a densitycomparable to that of a liquid and having a viscosity close to that of agas, but it also has a high degree of diffusivity so that it is ratherdifficult to prevent it from penetrating into sealing members or intogaps.

In this embodiment of the invention, a rack mechanism has been providedfor opening and closing the chamber 1; to that end, the lid 4 is hung bymeans of two brackets 15 and 16, each of which is provided at its upperend with a respective wheel 17 and 18 engaged with a rail 19.

Below the rail there is a rack 20 secured to the two brackets 15 and 16,which is engaged by a pinion 21 a of a drive motor 21 mounted on anexternal frame of the chamber 1, not shown in the drawings.

The chamber 1 illustrated in the drawings is completed by a drum 22which is arranged inside the cylindrical jacket 2, and a distributortube 23 for the carbon dioxide fed from a connector 24 passing throughthe wall of the cylindrical jacket 2; the distributor tube extends alonga generatrix of the cylindrical jacket and has a series of nozzles 25from which the carbon dioxide is delivered into the drum.

As regards the actual cleaning cycle of the items of clothing that iscarried out in the chamber 1, it takes place in known manner andtherefore only a brief account thereof will be given here whereas forfurther details, reference should be made to the relevant publicationsand patents mentioned above.

Carbon dioxide in the liquid or supercritical state is then introducedinto the cylindrical jacket 2 through the connector 24, while the tube23 together with the nozzles 25 distributes it in the drum which, tothat end, is produced with a perforated wall; with a suitable form ofthe nozzles 25, it is possible to direct the jets of carbon dioxidetangentially relative to the basket 22 in order to bring about therotation of the load present inside it (in this case garments), makinguse of the energy of the incoming fluid. Such a solution is alreadyknown in the art but it is, however, clear that it could be replaced orintegrated, for example, with a controlled rotation of the basket oranother form of agitation of the load while keeping the basketstationary.

The liquid or supercritical carbon dioxide then leaves the chamber 1(which is therefore provided with an outlet, not shown in the drawings)to be cleansed in the installation associated with the chamber, of themore or less soluble substances removed from the clothing.

At the start and at the finish of the cleaning cycle just described, theoperations of opening and closing the chamber 1 are carried out bycontrolling the movements of the lid by means of the rack mechanism, inaccordance with the following.

Owing to that mechanism the lid is guided accurately in its movements,so that the coupling of the two halves 5, 8 of the edge of thecylindrical jacket 2 with the corresponding halves of the lid 4 takesplace without interference and with maximum simplicity; in thisconnection, it should be remembered that in order to provide the chamber1 with a good seal, the precision of the coupling between the lid andthe cylindrical jacket has to be high and, owing to the guided slidingof the first relative to the second in the invention, it is possible tosatisfy such a condition.

It will also be noted that the guided sliding enables the cleaningchamber to be closed while avoiding slipping of the lid on the mouth ofthe cylindrical jacket, with all the obvious negative consequences thatthis fact would involve.

It should also be noted that, in this particular embodiment of theinvention, the support of the lid by two (or also more) brackets 15 and16, holds it rigidly in position during its translations along the rail19, preventing it from oscillating in a pendulum movement.

Once the chamber 1 has been closed, the seal 10 is activated as shown inFIG. 4; that is to say, the seal is pushed towards the opposite surfaceof the lid by the fluid which is injected into the recess 11, while, atthe same time, the pressure in the chamber 1 increases owing to thesupply of carbon dioxide thereto.

At this stage, the lid 4 is moved upwards (with reference to FIG. 4) bythe pressure of the CO₂ acting on it, which promotes the engagement ofits rib 7 a in the step 6 of the edge 5 of the cylindrical jacket 2.

It should be pointed out here that under such conditions the seal 10produced using the above-mentioned materials has demonstrated theimportant capacity to become deformed in such a manner as to provideoptimum sealing of the space between the lid 4 and the mouth of thecylindrical jacket 2, while at the same time resisting the thrustdirected onto it radially by the operating pressure of the carbondioxide.

In order to open the chamber 1, the above procedure is reversed.

Therefore, to begin with, the pressure inside it is gradually reduceduntil it is returned to atmospheric level, while the seal 10 is alsodeactivated; at that point, it is possible to disengage the rib 7 a fromthe step 6 and the lid can thus be removed, bringing about thetranslation thereof using the rack mechanism.

In this connection it will be appreciated that, if the pressure insidethe chamber 1 does not decrease to an extent sufficient to permit thedisengagement of the rib 7 a from the step 6, these two elements willprevent the lid from sliding and therefore the opening of the chamberwill be automatically prevented: this is therefore a special intrinsicsafety feature of the invention, that is to say, it is not necessary tohave an external control system having suitable sensors for detectingthe pressure inside the chamber in order to cause it to function.

It will therefore be appreciated that such a safety feature can also beused in the event of any breakdown or malfunction of the above-mentionedgeneral control system, preventing the inadvertent or premature openingof the chamber and thus contributing to its greater safety.

From the foregoing, the important results obtained by the cleaningchamber according to the invention will be appreciated.

Owing to the special configuration of the edges 5, 7, 8, 9 of thecylindrical jacket 2 and of the lid 4, according to which the edgesextend circumferentially and over half of that extension, one has asubstantially C-shaped cross-section that defines a seat wherein theother is accommodated and vice versa, the lid 4 can be held firmly andsecurely on the cylindrical jacket despite the substantial operatingpressures of the cleaning chamber.

The lid is then fitted in an accurate, simple and rapid manner owing tothe fact that it is guided slidably in a plane transverse to thecleaning chamber; the sliding of the lid also lends itself veryfavourably to the use of control means for opening and closing thecleaning chamber, of which the rack mechanism discussed here is clearlyonly one possible example.

It should be pointed out here that the use of structural elements havinga C-shaped profile and coupled to mating edges for the firm positioningof the lid, is already known in the field of sterilisation autoclaves asdemonstrated by the Italian patent No. 1237645, in the name of the sameapplicant for the present application.

However, in the field of sterilisation the pressures involved aresubstantially lower than those required for the CO₂ apparatusesconcerned here (3-5 bar instead of 30-80 bar), and therefore it ispossible to produce autoclaves having a parallelepipedal body instead ofa cylindrical body as required for cleaning chambers; some examples ofsuch autoclaves are given in the above-mentioned Italian patent.

Owing to the parallelepipedal shape of those autoclaves, their C-shapedelements for closing the lid are rectilinear: thus, some of them, inaddition to being used as locking elements for the lid in order toprevent it from becoming detached from the body of the autoclave, arealso used as guides when the lid is caused to slide transverselyrelative to the autoclave during its closing and opening operations.

In other words it may be said that in the prior patent, some of theC-shaped elements together with a portion of the edge of the lid of theautoclave substantially form a linear sliding pair able to guide thetransverse sliding movements of the lid and, at the same time, to ensurethat the lid is closed.

However, in cleaning chambers for carbon dioxide apparatuses, such asolution is not possible because the geometry involved is cylindrical(since, as already stated, it is made necessary by structuralrequirements) and therefore it is clearly not possible to form a linearsliding pair of the above-mentioned type between the edge of the jacketand the edge of the lid.

Consequently, in an entirely novel manner, the above-mentioned edges 5,7, 8 and 9 are used in the chamber 1 of the invention purely to ensurethe firm positioning of the lid 4 relative to the jacket 2 in order toprevent the lid 4 from becoming detached owing to the pressure of theCO₂, while the function of supporting and guiding the lid during theclosing and opening stages is performed by suitable means (that in theprevious example are provided by the rack mechanism but which could alsobe different, as will be seen hereinafter) not used, however, to attachthe lid to the cylindrical jacket.

Moreover, in the embodiment of the chamber 1 referred to above, thesemeans allow wide movements of the lid transversely to the cylindricaljacket in order to leave the mouth thereof practically free because,owing to the above-mentioned cylindrical geometry, it is not possible toattempt to combine small lateral movements with a subsequent “hinged”tilting of the lid as occurs in the case of autoclaves since, otherwise,the edges 5, 7, 8 and 9 would interfere with one another, therebypreventing such tilting.

In addition to such important results achieved by the invention, thecontribution made by the special seal 10 should also be emphasised.

As stated, the seal has a cross-section tapering towards the lid inaccordance with teaching already known in the art: this permits thebetter return of the seal into the associated accommodating recess whenthe fluid previously injected therein is discharged.

The above-mentioned tapered shape does not create difficulties whenfitting the soft seals into their accommodating recesses, used in thecase of containers for fluids that do not have the characteristics ofliquid or supercritical carbon dioxide.

Indeed, as already explained, such a fluid is a very effective solventand has, above all, a great molecular diffusivity so that it is ratherdifficult to contain it: in fact, the materials normally used for seals(such as silicone and the like), although chemically compatible withCO₂, tend to be penetrated thereby.

Other materials such as PTFE or derivatives, although suitable per sefor containing supercritical CO₂, have been found to be insufficientlyresilient so that the mounting of the seals having a taperingcross-section in the accommodating recesses was not practicable. FIG. 4shows that the accommodating recess also has a tapering shape and,because the corresponding seal has to be introduced into it from above,it will be appreciated that its larger base cannot pass through the openupper portion of the recess.

The epichlorohydrin rubbers mentioned above, in addition to beingcapable of containing supercritical CO₂, also have a certain resiliencewhich makes it possible to deform them in such a manner as to enable theseals formed therefrom to be mounted in the corresponding accommodatingrecesses, even if their cross-sections are tapered.

Naturally, it is also possible to have variants of the invention withrespect to the embodiment thereof which has been discussed hitherto.

The mentioned embodiment indeed is intended mainly for large cleaningchambers, such as those used in laundries or other services whichrequire the cleaning of large amounts of clothing or other objects ingeneral.

The horizontal arrangement of the longitudinal axis of the chamberfacilitates the work of an employee in carrying out the operations ofloading and unloading it; these operations are also helped by the factthat, in accordance with the invention, the lid 4 closes the entiremouth of the cleaning chamber which is thus completely freed when thelid is removed.

In other words, the lid is not simply a porthole or the like throughwhich a limited and difficult access to the inside of the cleaningchamber may be obtained, but in practice it constitutes a true removableend face, opposite to the fixed bottom face 3, which is fitted on themouth of the cylindrical jacket and whose opening permits optimum actioninside it. This is all the more important if it is borne in mind thatthe cleaning chamber is a container that has to withstand high operatingpressures.

Nor should it be forgotten that the horizontal arrangement of the axis Lenables a person to work from the front at the mouth of the chamber andtherefore more comfortably compared with the case of a large chamberhaving an upright axis.

In addition, in cleaning chambers of a certain size the lid is heavy andtherefore the possibility of hanging it on a horizontal guide structureas in the example mentioned, simplifies its handling which canoptionally also be effected manually and not purely mechanically.

However, the situation would be different in the case of a hinged typelid because, if the cleaning chamber is large, its weight and theinevitable space required for the opening and closing operations couldgive rise to relevant difficulties for an operator, as well as the useof a control mechanism would appear to be rather complex.

A further substantial advantage of the invention resides in the factthat the means provided therein for supporting and guiding the lid, thatis to say, the rail and the rack mechanism of the previous example, areseparate from the cylindrical jacket: this prevents overloading of thestructure of the jacket which would otherwise have to have dimensions(above all a thickness) suitable for bearing the weight of the lidwhich, in the case of chambers of a certain size, is certainly notinconsiderable. Since the cylindrical jacket, the associated bottom andthe closing lid are produced from special materials (preferablystainless steels) which are thus also expensive, such a cleaning chamberenables the use of those materials and thus the costs derivingtherefrom, to be reduced.

An alternative embodiment of the invention suitable for small cleaningchambers is shown in FIGS. 6 and 7 where the chamber is generallyindicated 101.

This embodiment will be described briefly hereinafter with particularreference to its main differences from the previous one; however, forthe sake of simplicity, elements that are structurally or functionallyequivalent to those already considered will be designated by the samenumbers and will not be analysed further in detail, attention beingdrawn to the explanations provided above for that purpose.

As will be appreciated, the cleaning chamber 101 is in this case of thetype having an upright longitudinal axis L and is closed by a lid 4guided slidably in a direction transverse to that axis.

However, in this variant the lid 4 rests on two sliding blocks 102, 103movable along respective parallel guides 104, 105 arranged on oppositesides relative to the lid. More especially, the lid 4 is connected tothe sliding block 102 by means of a hinge 106 and a radial arm 107 inorder to be able to pivot about an upright axis V; diametricallyopposite that arm is a peg 108 which projects radially from the lid andwhich is supported by the sliding block 103.

The edges 5, 7, 8, 9 of the cylindrical jacket 2 and of the lid 4 arecoupled to one another owing to the shape of their cross-sections alongrespective semicircles in a manner entirely similar to that alreadyexplained; in this second embodiment of the invention, however, the lid4, in addition to being translated solid with the sliding blocks 102 and103 in a plane transverse to the longitudinal axis L, is also able topivot in that plane owing to the fact that it is hinged to the slidingblock 102, as shown in FIG. 7.

Consequently, the operations of opening and closing the chamber can takeplace either by translating the lid 4 (as shown in FIG. 6), or bycausing it to pivot about the axis V (as in FIG. 7), or by combiningboth these movements.

It will therefore be appreciated from the above that this furtherembodiment of the invention also achieves the important results of theprevious one and consequently, for the sake of brevity, on this subjectreference should be made to the explanations provided in connection withthe first embodiment, naturally giving due consideration to thedifferences concerned.

It just has to be pointed out here that this variant does not providefor means of controlling the movements of the lid, given that, for smalldimensions of the cleaning chambers, the operations of closing andopening can be readily carried out manually; it is, however, clear thatthe presence of such means should not be excluded.

It should also be noted that the possibility of pivoting the lid isparticularly suitable for cleaning chambers having an upright axisbecause these chambers do not involve the risk of pendulum movements ofthe lid caused by the force of gravity, as occurs in chambers having ahorizontal axis.

Finally, referring to FIGS. 8-10, brief mention will now be made of thecompressor 36 operated by liquid CO₂, which was discussed above.

The compressor has a double-action piston 40 which is configured as anannulus and is movable in a central casing 41 supplied with liquid CO₂that, in the case of the apparatus of FIG. 1, comes from the tank 30.

In particular, the liquid CO₂ enters and/or leaves by two openings 42,43 communicating with a distributor 60 shown in FIG. 9, as will beexplained later.

The double-action piston 40 is mounted on a tubular sleeve 45 which isclosed at its ends by two discs 46, 47 sealingly coupled to the walls oftwo cylindrical chambers 48, 49, arranged at the sides of the centralcasing 41; the cylindrical chambers 48, 49 are closed by an end face onthe side remote from the above-mentioned discs and are each providedwith an inlet valve, 50 and 51 respectively, and with an outlet valve,52 and 53.

The valves are used for the intake and delivery of gaseous CO₂ which, inthe case of the apparatus of FIG. 1, comes from the cleaning chamber 1and is either delivered to the tank 30 or is returned to the chamber 1,as occurs in the case of the valves of normal internal combustionengines.

The functioning of the compressor just described is quite simple.

The high-pressure liquid CO₂ coming from the tank 30 is admitted intothe central casing 41 through one of the two openings 42 and 43; in thatsituation, the other opening is not charged with the pressure of thetank and the piston 40 can move from right to left or vice versa,depending on the difference in pressure of the liquid CO₂ acting on itsopposite faces.

The alternating movement of the piston 40 is transmitted to the sleeveon which it is mounted and, therefore, the discs 46 and 47 arranged atthe ends of the sleeve move inside the cylindrical chambers 48, 49 inthe manner of plungers, sucking in and compressing gaseous CO₂ whichflows through the valves 50, 52 and 51, 53.

The switching of the supply of liquid CO₂ at the openings 42, 43 andtherefore the control of the stroke of the piston 40 can be effected invarious manners, for example by providing sensors in the compressor andby controlling the supply electronically by means of servovalves.

However, in accordance with a preferred embodiment of the invention, theswitching is carried out using the electromechanical distributor whichwill now be explained briefly.

The distributor 60 is in practice formed by a cylindrical housing 61closed at the ends and in which is mounted a rotor 62, splined onto adrive shaft 63 protruding from one end of the housing 61; a drive motor(not shown in the drawings) is arranged on the shaft.

In the area of a median transverse plane of the cylindrical housingthere are formed two pairs of apertures 65 and 66 which are arrangeddiametrically opposite one another and which connected, respectively, tothe tank 30 of high-pressure liquid CO₂ and to an outlet at lowerpressure.

Similar apertures 67, 68 are arranged along two other transverse planeswhich are located at the sides of the above-mentioned median plane andare in communication, respectively, with the inlet openings 42, 43 ofthe compressor 36.

The rotor 62 has four lobes 70 which, as a function of its rotation,bring the pairs of apertures 65 and 66 into communication, respectively,with the two apertures 67, 68 and thus with the openings 42, 43.

Consequently, depending on the angular position of the rotor, liquid CO₂enters or leaves through the openings 42, 43 of the compressor atdifferent pressures (that is to say, the pressure of the tank 30 and thepressure of the outlet connected to the apertures 66) so that theopposite faces of the piston are acted upon by a differential pressuresuch as to cause it to move back and forth in the central casing 41.

What is claimed is:
 1. An apparatus for cleaning using a dense phasefluid circulating therethrough, the apparatus comprising: a cleaningchamber comprising a cylindrical jacket having at one end a fixed bottomand being closed by a removable lid at the opposite end, wherein the lidis surrounded peripherally by a circular edge having first and secondsections to be applied on corresponding first and second sections of anedge of the open end of the cylindrical jacket; the open end of thecylindrical jacket and the lid defined by the first sections of theirrespective edges each having a longitudinal extension substantiallyequal to half their circumference and a substantially C-shapedcross-section, which sections are suitable for receiving, respectively,the second sections of the corresponding edges of the lid and of theopen end having a mating shape; the lid being supported by means outsidethe cylindrical jacket in such a manner as to be movable transverselythereto between a first position in which it is at a distance from thejacket, leaving the open end thereof substantially free, and a secondposition in which the lid closes that end by engaging with the edgethereof; a tank for the fluid; a distiller; a refrigerating unit;pumping means; and means for filtering the fluid, wherein during atleast part of a cleaning cycle, the dense phase fluid supplied by thepumping means along a path from which the tank and the distiller areexcluded, circulates through the cleaning chamber.
 2. An apparatusaccording to claim 1, wherein the lid of the cleaning chamber isslidably supported by guide means so that it is movable between thefirst and second positions as a result of its sliding guided by thosemeans.
 3. An apparatus according to claim 1, wherein the lid of thecleaning chamber is supported by hinging relative to an axis (V)parallel to that (L) of the cylindrical jacket, and is slidablysupported by guide means so that it is movable between the first andsecond positions as a result of at least one of its pivoting about thataxis and its sliding guided by those means.
 4. An apparatus according toclaim 3, wherein the hinge axis (V) of the lid and the axis of thecylindrical jacket are upright.
 5. An apparatus according to claim 1,wherein the cleaning chamber comprises at least one seal between the lidand the cylindrical jacket, which seal is made from epichlorohydrinrubber.
 6. An apparatus according to claim 5, wherein the at least oneseal is accommodated in a recess formed along the first and secondsections of the edge of the cylindrical jacket and both have across-section tapering towards the lid.
 7. An apparatus according toclaim 6, wherein the at least one seal is activated with the cleaningfluid present therein.
 8. An cleaning apparatus according to claim 1,wherein along at least one of the portions of the second section of oneof the lid and the cylindrical jacket which engage with thecorresponding first sections having C-shaped cross-section, there isprovided a rib suitable for engaging in a step of the other section inorder to prevent the movement of the lid from the second to the firstposition, when the pressure in the cleaning chamber is greater than apredetermined value.
 9. An apparatus according to claim 1, wherein thefixed bottom and the lid of the cleaning chamber are convex.
 10. Anapparatus according to claim 1, wherein the means for guiding the lidcomprise a rack drive mechanism which can be adjusted in such a manneras to limit the closing force to levels safe for a user.